Communication system



Nov. 10, 1942. N. H. suREN ETAL COMMUNICATION SYSTEM 5 Sheets-Sheet 1`Filed Jan. 4, 1940 TPI/111) TIPP' Y l ramw.;

Nov. 10, 1942. N. H. suREN ETAL 2,301,475

COMMUNICATION SYSTEM Filed Jan. 4, 1940 V 5 SheetS-Sheel 4 Nov. l0,1942. N. H. sUREN FAI. 2,301,475

COMMUNICATION SYSTEM Filed Jan. 4, 1940 5 sheets-sheet 5 yl yf l WMPatented Nov. l0, 1942 UNETE STATES 'iliiii @FREE CMRIUNCATGN SYSTEMApplication January 4, 1940, Serial N 312,350

(Cl. Z50-S) 7 Claims.

The subject of the present invention is a method of transmitting privateor secret signals or messages by public channels of communication, i.e., radio waves and telephone wires. Its object is to enable radiofrequencies, which may be in use simultaneously for public broadcastsand other purposes, or telephone lines which also may be in use forordinary purposes, to be used Without interruption of, or interferencewith, their normal functions, for the transmission of code messages,signals, etc. to selective receivers. A further object is to provide ameans of exclusive selectivity whereby a signal intended for one denitereceiver, and only the signals so intended, will be received by thatreceiver only. A further object is to devise a system of code signaltransmission whi-ch cannot be readily intercepted, and of which theprobabilities of successful decoding are so small as to be practicallyan irnpossibility. A still further object is to provide means by whichsuch a code message may be sent and recorded by the authorized receiverin intelligible form requiring no subsequent decoding.

Other and related objects are set forth in the following explanation ofthe invention.

In its generic aspects the system of this invention consists ingenerating a group of mechanical vibrations (within which term weinclude sound vibrations) of two or more different frequencies, whichmay be audible or inaudible frequencies but are within the range ofselectivity of available selectors; interrupting such vibrations at suchintervals of time that their persistence between interruptions is verybrief, but only while all the vibrations of a given group are beinggenerated simultaneously; converting such mechanical vibrations intoelectrical vibrations either by a wireless transmitter or a telephonetransmitter; receiving the vibrations in a group of tuned selectors ofwhich each selector is responsive to the vibrations of one frequencyonly; converting the received vibrations into mechanical motion; andcausing such mechanical motion to operate a recording instrument ordevelop souni waves.

The vibrations at the transmitting end are produced intermittently, orinterrupted, according to a predetermined code of signals and theimpulses converted by the receiver reproduce the signals audibly or on aprinting recorder, or both. The code may be the common dot and dashsystem or impulses utilized according to some predetermined plan tooperate a printing apparatus Illustrative embodiments of the principlesthus briefly summarized are described and explained in the followingspeciiication and illustrated in the accompanying drawings.

In the drawings,

Fig. lis a diagram of a complete wireless transmission system embodyingour invention;

Fig. 2 is a diagram of one form of selector adapted to be tuned to lterout all vibrations except those of one given frequency, within anextremely narrow range;

Fig. 3 is a rear elevation and Fig. 4 a side view of a signal generatingmachine organized to formulate code messages for transmission accordingto this invention;

Fig. 5 is a partial development of the type wheel used in this machineand in the recording machine subsequently described;

Fig. 6 is a rear elevation and Fig. 7 a side elevation of a recordingapparatus adapted to print intelligibly code messages transmittedelectrically from the sender shown in Figs. 3 and 4;

Fig. 8 is a diagram showing a system organized to receive selectively atdiierent points signals sent by means of vibrations of six differentfrequencies used three at a time simultaneously;

Fig. 9 is a diagram showing a simplification of yne reeciving end of thesystem shown in Fig. -8 where a group of recorders are located in suchproximity to one another as to be controllable by mechanically connectedswitches;

Fig. 10 shows the receiving end of a system such as that represented inFig. 8, with modifications enabling the recorders to be activated bygroups of three vibration frequencies when the different vibrations areinitiated progressively as distinguished from simultaneously,

Like reference characters designate the same parts wherever they occurin all the gures.

The system represented by Fig. l consists of a sending stationdesignated as a whole as A and a receiving station designated as a wholeas B. The equipment of the sending station comprises a vibrationgenerator a, a signal instrument b, an amplier c, which may be omittedwhen amplication is not needed, and a transmitter cl For wirelesstransmission the transmitter may be any L :ncwn producer of radio wavesconnected with an antenna e. For signalling over a telephone circuit,the ordinary telephone transmitter will serve. The vibration generatorand signal sender may be combined in one instrument as will presentlyappear.

The `vibrations generated for this purpose may be of any frequencieswithin practical limits. That is, the lowest frequency possible to beused is limited by the selectivity of the receiving selector,its abilityto isolate a given frequency from adjacent frequencies And the highlimit in radio transmission is established for practical use by the lawfixing the band width between channels. As the difference between radiofrequencies is fixed by law at 10,0G0Vcycles per second, the highestimposed frequency permissible for our system under present laws is 5,000cycles per second. But in principle the highest frequency usable islimited only by the qualities of the selector.

It will be seen therefore that in practice our controlling frequenciesare limited to those within the audible range, although in principlethey may be outside of that range.

Vibration frequencies corresponding to the notes of the chromatic scale,or with intervals between frequencies equal to those between notes ofthat scale, may be used. for we have found it feasible with availabletuning means to make selectors capable of discriminating between notesone half tone apart. Thus the notes of the standard scale, orintermediate tones, with sufficient intervals between tones of theseries, may be used for our purpose. We will in the followingdescription refer at times to the frequencies herein discussed as tonesor notes.

Such tones may be produced by any one of many well known means, such astuned strings, reeds, forks, pipes, sound records, etc., and may beproduced intermittently at longer or shorter time intervals like orproportional to those of the dot and dash code. Or the sound vibrationsmay be converted into electrical undulations or vibrations andinterrupted intermittently by manually or automatically operated meansto produce dot and dash code signals.

The conversion of mechanical vibrations into the correspondingelectrical equivalents and modulation of the radio carrier wave by suchelectrical vibrations are effected by the standard equipment used forradio broadcasting or any other suitable means known to radio engineers.As standard equipment is suitable for the transmission, and also thereception, of the radio wave modulations in the performance of ourinvention, we have deemed it unnecessary to show the transmitteramplifier or receiver in detail.

The receiving station comprises a receiver f, which may be the same asany standard radio receiver capable of being tuned to carrier waves y ofdifferent frequencies, a selector g by which the controlling frequenciesof our invention are segregated from other frequencies. a collection ofrelays and switches in circuit with a source of power, allcomprehensively designated by h, and a recorder z'. The selector,relays, and recorder are hereinafter more fully described.

The foregoing description is suflicient for an understanding of thebasic principles of the invention. It will be understood that group oftwo, three or more different frequencies, which will be assumed for thepurposes of this description to be those corresponding to any differentmusical notes, are produced with interruptions by the generatingandisignalling means a, b. At the receiving station these vibrationsactivate an equal number of tuned selectors, and only selectors whichare tuned to those specnc frequencies.

Relays operated'by the energy delivered from the selectors lcloseelectric circuits Venabling power from a battery or other power sourceto initiate mechanical impulses by which effects 'corresponding to theoriginal signal are obtained.

, Selectors capable of being tuned within close limits to' specic tonesare known, and in Fig.

2 we have shown illustratively one which is suitable for our purpose.This includes a transformer T of which the primary winding y isconnected to the receiver f so as to carry the radio frequency with allits modulations. The secondary winding Ic of this transformer isconnected with a bridge l, one arm of which con-f Vthe secondary windingn is connected to the relay. To obtain the selected note in usable form,

an auxiliary circuit o is used, having a winding p arranged as asecondary to the transformer T, a winding q arranged as a primary to theoutput transformer T2 and in opposition to the winding m, and a volumecontroller 1. This auxiliary circuit passes all tones received by theinput transformer T. By setting the volume controller r so that theelectrical waves in the two circuits have the same intensity, then, asthe primaries m and q are in opposition, the same frequencies in eachcircuit will cancel out, and only the selected frequency will issue fromthe secondary winding of the output transformer. Each receiving stationis equipped with as many such selectors as the number of tones used 'forcontrolling it. Other selectors than the specic one illustrated may beused within the scope of our' invention. This illustration is intendedto typify by one concrete embodiment the generic idea of a tunedselector.

An illustrative embodiment of vibration generating, signal sending, andsignal receiving means is shown in Figs. 3 7 similarly typifying thegeneric idea of means forthis purpose. The generating and sendingapparatus is shown in Figs. 3 and fl. It includes a source of mechanicalpower H, which may be a spring motor, an electrical torque motor, or anyother prime mover capable of being stopped instantly when obstructed andof starting instantly when released and is regulated to run at aprescribed rate of speed. It drives through a gear train l2, i3 aphonograph disk l on the circumference of which is a track or groovehaving a predeter-4 mined number of like wave groups spaced apart fromone another. Each wave group is the resultant of two or more vibrationfrequencies, like any phonographic record of a musical chord. When thedisk is set in motion its track vibrates a needle l5, such as aphonograph needle, which operates an electrical pick up I6, from whichelectrical undulations are conducted to the transmitter d of Fig. l tomodulate the radio wave. This part of the apparatus may be the same asthe means employed fer broadcasting phonographic transcriptions;

The disk I4 is coupled by a speed reducing gear train l1, I8, I9 and 2Gto a shaft 2! on which are mounted a type wheel 22 and a drum 23. Thisdrum is associated with a keyboard (Fig. 4) having keys 245 analogous totypewriter keys, each of which is carried by a lever 25. All the keylevers are pivoted side by side on a shaft 25 and each is coupled to astop lever 2l by suitable means such as gear teeth 23 on a second arm ofthe stop lever and on a portion of the key lever respectively. All ofthe stop levers 27 are mounted side by side on a shaft 29 parallel tothe shaft 2l, and each has a toe 30 adjacent to the circumference of thedrum. Individual springs 3l are connected to the several key levers andto a stationary anchorage in a manner to hold the keys normally raisedand the stop levers El normally withdrawn from the circumference` of thedrum. When any key is depressed its corresponding stop lever is movedtoward the surface of the drum. Each key lever has a rearwardlyextending arm 32 which is raised when the corresponding key isdepressed, and is formed with a cam surface 33 beneath a latch bar 34.The latch bar is suspended by arms 35 at its opposite ends from a pivotshaft or pivots 35 and is located in a position such that rise of anykey lever arm 32 dispiaces it rearwardly and the arm is able to passclear of the latch bar while its'associated stop lever approaches thedrum 23. A spring 3'! is provided to return the latch bar after any ofthe arms 32 has passed it, and thus retain this arm in raised position,and the associated stop lever 21 in position near the drum, until thelatch is again displaced by op.- eration of another key or by othermeans.

The drum carries outwardly `projecting stops 38, each in the same planeperpendicular to the axis of the drum with one of the stop levers,whereby any stop lever when advanced by depression of a key is enabledto arrest the rotating drum. Preferably there are two, three or more ofthe stops 33 in the same plane with each stop lever in order to increasethe difficulty of deciphering intercepted code messages. Such stops maybe made as pins set into the circumference of a continuous drum, but forsimplicity and ease of manufacture, the drum is preferably made of aseries of disks equal in number to the stop levers 2l and equally spacedtherewith,

keyed to shaft 2l and made with projections.4

forming the stops 38 in suitable angular relationship with theprojections on other disks.

The type wheel 22 carries printing types on its circumferencerepresenting characters such as the letters of the alphabet, thenumerals, and marks of punctuation; or other characters or symbols whichmay be used conventionally or arbitrarily as a means of intelligiblyrecording. corriiriunicationsl Each key is appropriated to one of suchcharacters or symbols, and the stops 38 on the drum 23 are located insuitable angular relationship to the characters on the type wheel and tothe stop levers so as to arrest the type wheel with any selectedcharacter in a predetermined zero position when the key corresponding tothat character is depressed.

The aero position referred to may be that which enables a printed recordtoV be made of the seiected character, and in the present illustrationis the uppermost point of the wheel. A printing attachment is here shownconsisting of a paper tape 39 passing from a supply roll 4B to a take uproll 4I around guide roils 42 located near the type wheel, an inkedribbon 43 passing between the type wheelv and paper around guide rollsM, and a hammer '35 at the outer side of the paper adapted to strike thepaper and ribbon against the type which is in zero position.

For conveying intelligence by means of the Roman alphabet and Arabienumerals, with punctuation, a total of about forty, or a few more,characters is suiicient. But to increase the difficulty oi deciphering,two or more series of characters are provided in which the charactersare arranged in different sequences. For instance, the characters may bearranged in conventional order in one series, in inverted order inanother series, and in jumbled order in still another series; or theymay be differently jumbled in two or more series. But however they maybe arranged, the stops 38 which cooperate with any one stop lever arespaced so that whenever the key related to that stop lever is depressed,the corresponding character in one or another series will be arrested inthe zero position. In other words, all stops 38 of the same disk, or inthe same Zone of the drum, are separated from one another with anangular spacing equal to that between the repetitions of the samecharacter on the type wheel.

Each key, when depressed, releases the stop lever previously inarresting positiorrby disf placement of the latch bar effected throughthe cam surface on the rear arm 32 of the key lever. In order that therelease of a previously latehed key lever shall certainly occur, thehanger arms 35 carry a second b ar 34a at a height above the bai' 34suicient to permit entrance between them of the extremities of the arms32, The bar 34a has an inclined under surface located where it will beengaged by the key lever arm 32, when the key is fully depressed, and bethen displaced so as to hold the latch bar 34 clear of the key leverarms. Such cooperation of any key lever arm 32 with the bar 33acontinues until the corresponding key is released after being depressedand insures opportunity for a previously latched key lever to returninto normal position before the latch bar returns into latchingposition. But the latch is returned by its spring 3l into arrestingrelation to the key lever last operated as soon as the key is releasedby removal of the operators finger from it.

An electromagnet ll is connected in circuit with a source of electricenergy, indicated in Fig. 4 as a battery cl, and with a switch orcircuit closer t8. This magnet serves to operate the printing attachmentand to open its own circuit after so operating. The switch is normallyopen, having an arm 49 carrying one contact, which is spring biased soas to separate from the complemen'tal contact, For closing the switchthere is provided a loosely pendent lever arm 5u carried pivot-ally by alever 5i pivotcd at 52 to a fixed part of the framing or supportingstructure (not shown). A spring 53 reacting between a part of thecarrier lever 5l and the pendent arm E holds the latter against theextremity of the switch arm 4S and causes it to swing over the upperside of such extremity when raised. An extension on the lower extremityof arm 55 limi-ts its movement in that direction by coming to bearagainst the end of switch arm The carrier lever 5i is i Lisedpreparatory to closing the switch by a ratchet wheel 5G with which apawl element or tooth 55 on the carrier arm engages. Ratchet 54 .issecured to a shaft 56, which latter is rigidly connected coaxially withthe gear i? phonograph disk lf3, extends through a central bore in theshaft 2l, wherein it has a rotative bearing. The ratchet wheel has asmany teeth as the phonograph disk has Wave groups, and its teeth arerelatedl to the pawl element 55 so as to raise the carrier lever as eachsuch group passes the pick up needle, thereby placing the switch closinglever in operative position with the 'fst movement of the mechanismfollowing depression of key. But closing of the switch is not effecteduntil the carrier lever descends when the mechanism is arrested by one(any one) of the stop levers 2l.

lever l by a gear sector Si! on the lever and a pinion 5l loose on theshaft of the escape wheel,

with which latter it has a one way driving connec'tion by means of apawl E2. Rise of lever 5| turns the pinion El without turning the escapewheel, but descent of lever 5l causes the escape wheel to turn, therotation of which is retarded by the pallet. Such retardation ispredetermined to prevent descent of the lever 5G far enough to close theswitch before it is again lifted by a iollowing tooth of ratchet Eli.But. when the drum is arrested (at which time the phonograph disk andratchet wheel are also arrested) timey is afforded for the switch to beclosed.

The armature 5H of the magnet dais carried by a pivoted lever having anarm 52| by which the printing hammer t5 is carried. Closing of theswitch le therefore causes t'he hammer to press the paper and inkedribbon against the type wheel and make an imprint. An extension 531 ofthe armature lever pro'trudes so that its path crosses a cam portion ofan arm 55a forming part oi the switch closer 56 wherefore the movementimparted to the extension 53| by the magnet displaces the switch closerand allows the switch to open by its own spring action.

Thus the circuit is closed whenever the movement of the type wheel isarrested, and opened as soon as printing has been effected. The operatoris informed by visible or audible evidence of the operation of thisprinting attachment when the next letter of the message may betransmitted by depression of another key. He may not depress such otherkey until the printing attachment is operated in response to the actionof the key last previously depressed, because to do so would causefailure to record the last transmitted letter at the receiving station.It is within our contemplation to provide automatic means under controlof the magnet or its armature lever for preventing actuation of a keyuntil after the printing attachment has operated, as by blocking thelatch bar 3i so that it cannot release the key levers; but we regardsuch automatic obstruction as nonessential in View of the definiteindi-cation given to the senses oi the operator by the printingattachment in its movement. The delay of such movement caused by theretarding escapement 58, 5e gives time for operation of the recordingprinter at the receiving station,

A lever 51M, which we call a synchronizing stop lever, is provided tocorrelate the type wheel of the recording instrument (later described)at the receiving station with the type wheel of the sending instrument.This lever is connected to the shaft 25 beside the end of drum 23 bymeans of a pin 55! so that it may swing in two directions, i. e., aboutthe axis of the shaft and toward and away from the adjacent end of thedrum. It has a short arm 55! arranged to coact with a synchronizing stop57| on the adjacent end of the drum and a finger or blade 58! arrange toengage the threads of a screw or worm 59| on shaft 2l. A spring 63 isconnected to this lever tending to hold the blade in engagement with thescrew, and a spring 55 acts on the lever with tendency to withdraw thearm 55| from the synchronizing stop 5H. Preferably a single spring isused in practice for these purposes, arranged to act approximately onthe line of the resultant of the forces exerted by the springs 63 and54, but for convenience of illustration in diagrammatic drawings such asthese, we have shown two springs. It is within the skill of the machinedesigner to mount properly the above described equivalent single spring.The synchronizing lever has a cam or wedge portion 64| with whichcooperates the extension of an arm 65| connected to the nearer one Vofthe suspension arms or hangers 35 which carry the latch bar. Thearrangement of these parts is such, as shown in Fig. 4, that when anykey is depressed, the consequent movement of the latch bar causes arm todisplace the synchronizing lever from engagement with the screw 5SH,whereupon the arm 561 is withdrawn from the synchronizing stop 5?! andthe drum is left free to be rotated.

The stop lever may be so displaced, not only by the regular keys, butalso by a special key 65, which we call a synchronizing key, carried bya key lever 65 which is like any other key lever except that it has nomeans for actuating a stop lever 21 and is not coupled to any suchlever. But it has a rear arm 32| which, when the key is depressed,causes the latch 34 to be displaced and the synchronizing leverdisengaged as just described. When the latch returns to normal position,the stop lever is permitted to engage the screw 5SH at a point axiallyremoved to the right (with respect to Fig. 3) from its point of previousengagement, whereby rotation of the drum feeds the lever back toward itsarresting position. In this embodiment such displacement is equal to thelead of two turns of the screw so that the drum may rotate, before beingarrested by the stop lever, through an angle enough greater than onecomplete turn to insure placementJ of the type wheel of the receivinginstrument in zero or starting position from whatever position it mayhave been left in at the end of a previous message. A suitably locatedstop pin or shoulder (not shown) limits the displacement of the stoplever to the distance above mentioned.

The displacement of the synchronizing stop lever similarly caused byoperation of the regular type keys ensures against interference by thesynchronizing stop with the rotation of the drum in sending a message.The greatest angular movement of the drum between any two stoppingpositions controlled by the levers 2 and stops 38 is less than onecomplete rotation, which is insufficient to cause return of thesynchronizing stop lever into obstructing position.

The signal disk i4 turns at a high rratio with respect to the typewheel, which is here represented as being 6 to 1 but may be ofothersuitable value. Thus a conveniently small phonograph disk having aconveniently small number of wave groups may be used with a type wheelhaving a large number of characters. There are as many wave groups asthe number of characters on the typ-e wheel divided by the speed ratio,and the several wave groups are spaced proportionaly to the spacing ofthe characters on the type wheel. As the motor is regulated to run at anexact speed, the electrical waves or modulations generated by each groupon the disk have the same frequencies as those produced by all othergroups, whereby an impulse effect is produced, with the traverse of eachwave group past the needle, at whatever receiving station is tuned tothe frequencies of these wave groups.

An apparatus for recording the messages sent by the sending apparatusjust described is shown in Figs. 6 and 7. This apparatus includes a typewheel 51 which contains exactly the same char-V acters in the samenumber and sequence as the characters of the type wheel 22. It is drivenby a prime mover 68, which may be a spring or electric motor, capable ofstarting instantly and of driving the type wheel and other parts of theinstrument at a suiliciently rapid rate; i. e., enough faster than thecorresponding parts of the sending instrument to compensate for theintermittent movement presently described. The motor is coupled bygearing 69, il) with a let off or escape wheel and the latter is gearedto the type wheel 6'! by a gear train T2, i3, M, 'l5 and shaft '16. Thelet off wheel has teeth equal in number to the number of wave groups onthe sending disk le; and the speed ratio between this wheel and the typewheel 6l is equal to the speed ratio between the sending disk |15 andthe type wheel 22 of the sending apparatus. The winding of anelectromagnet 'H is coupled to a source of electric power under controlof the tuned receiver whereby it receives a current irnpulse whenever anelectrical wave group is generated by the sending disk. The armature '8of this magnet is carried by a pawl lever 'i9 which is connected by alink 89 with a lever S2 which carries a pawl 8i. The two pawls are atdiametrically opposite sides of the escape wheel and separated from oneanother by a distance so 1e lated to the wheel teeth that, when eitherpawl is displaced clear of the wheel the other pawl is in a notchbetween two teeth. A spring 83 is connected to this pawl assemblagenormally tending, and eiective when the magnet is deenergized, to holdthe pawl 8| clear of the wheel and the pawl 'le in a notch between twoteeth. But when the magnet is energized the pawl 79 is disengaged andthe pawl 8| brought into engagement with the wheel. The pawl 8| ismounted on the lever i with provision for movement tangentially of thewheel a distance substantially equal to the tooth spacing by means ofpins 54 passing through slots in the pawl, and a spring 85 is connectedwith the pawl and lever in a manner to hold the pavvl at the limit ciits motion in the direction opposite to that of the adjacent side of thewheel. Thus the pawl is able to yield under the pressure of the motordriven wheel when brought into the path of any of the teeth thereofenough to permit rotation through the whole angle between adjacent teethwhen pawl 'E9 is withdrawn.

A printing mechanism is provided beside the type wheel consisting of apaper tape SS, an inked ribbon 8l and a hammer (i8 carried by a lever99, one arm of which carries the armature 9G of an electrcmagnet 9|, andis acted on by a spring 92 arranged to withdraw the armature from themagnet. This mechanism is substantially like that rdescribed inconnection with the sending machine. It may be understood withoutillustration that we employ in the oommercial instruments, both thesending and receiving instruments, known means for propelling the papertape after each impression a distance sufcient to avoid over printing ofone character on another.

The winding of the magnet di is connected in circuit with a source oipower, represented as a battery 93, and with a switch 9d. Said switchincludes a spring biased arm carrying one electrode and tendingconstantly to separate said electrode from the complemental electrode.It is controlled b-y a lever 99 pivoted at 99 and carrying a pivotedpendent lever |98 (like the lever 5i) of the sending instrument)lproject-ingtoward the switch arm 96 and closing the switch when loweredby descent, after rise, of the carrier lever. This lever has an upperbent arm 892 cooperating with an extension 89| on the armature lever 39as in the sending instrument. Gravity and a spring 98| tend to lowerlever 98. The pawl lever 82 extends toward lever 99 in such `proximityto a cam protuberance on the under side of the latter that, when movedby the magnet TI, as described, it engages this protuberance to preventswitch-closing descent of the lever. The switch controlling lever has agear sector |02 meshing with a pinion |93 which is loosely rotatable onthe shaft of an escape wheel |05 and has a one way driving connectiontherewith by a pawl m with the escape wheel |95. A pallet i cooperateswith the escape wheel. Rise of the sector turns the pinion withoutaffecting the escape wheel, but descent of the sector turns the escapewheel by means of the pawl and its rotation is retarded by the pallet.

A ratchet wheel |01 is connected rigidly with the let off wheel 'Il toturn at the same speed therewith and has the same number of teeth, butits teeth are inclined in the opposite direction so that they act as camelements. They are arranged to coact with a pawl tooth |68 on the lever98 so as to raise the latter whenever a tooth on the let oi wheel isallowed to escape past the pawl 18. The rise of lever 98 thus effectedis sufficient to raise the switch closing lever I 60 so that the step onits end which closes the switch 94 is above the spring arm 95 inposition to close the switch with subsequent descent of the arm. At eachmovement of the connected pawls to the left (with respect to Fig. '7)the arm 82 is brought under protuberance (1| While this arm and camprotuberance would sufce to raise the lever with each impulse of themagnet, we prefer to use the power of the driving motor through the camratchet |01 for that purpose -rather than to impose this burden on themagnet. But the protuberance may assist or supplement the cam ratchet inholding the lever in raised position. The delay caused by the retardingescape wheel prevents closing of the switch during the normal periodbetween impulses when two or more are sent in succession, preventing theswitch from being closed until the let off mechanism pauses aftercessation of impulses due to arrest of the sending instrument by themeans previously described.

The recorder also includes a synchronizing lever m9 pivoted transverselyto a supporting shaft i9 by a pin and having a stop arm ||2 cooperatingwith a synchronizing stop H3 on the type Wheel, a iingerror bladecooperating with a screw H5 on the printing wheel shaft l, and a longarm terminating in a cam face beside a projection H5 on the armaturelever. A spring ||1 holds linger |13 inengagement with the screw andpermits disengagement therefrom by the action of `pin H6 when theprinting magnet is energized. A spring 8 swings the lever aside aboutthe pivot and withdraws the arm l2 from the stop I I3 or an equivalentsingle spring operating on the resultant line of the efforts of thesetwo springs may be used. Each actuation of the printing magnet releasesthe synchronizing lever and causes it to re-engage the screw at a pointfar enough removed from stop ||3 to permit at least one rotation of theVtype wheel, but not so extensive a rotation as that permitted the drumof the sending instrument Vwhen its synchronizing stop is released. Thusthe printing of the last character of a message leaves this type wheelfree to be automatically correlated with the type wheel of the sendinginstrument.

In this disclosure of signal sending and recording means we have notattempted to show details of framing, bearings and other supportingmeans for the moving and stationary parts, but have contented ourselveswith a description of the principles of the machines and a diagrammaticillustration of their parts and an operative relationship between suchparts in as simple a manner as possible and with the least possiblenumber of drawings. This showing is sufficient for an understanding ofthe invention and to enable draftsmen and mechanics, using the commonknowledge and skill oi their respective callings to design and buildoperative oommercial machines.

In order that a message may be correctly transmitted by the instrumentshere described, they must be in correct correlation or coordination witheach other. Normally they are so related, particularly where in frequentuse, for the conclusion of one message leaves them in correct positionsfor sending the next one. But in case they are not, or if the operatorwishes to avoid any possibility of their being out of step, he depresses`the synchronizing key 65 of the sending instrument before sending themessage. releases the synchronizing stop 57| without imposing any otherstop in the path of the drum, and at the same time causes displacementoi any stop lever 27 which may previously have been in the path of astop 3B. The drum and sending disk I4 then rotate and a succession ofequally timed wave groups is transmitted, causing the type wheel of therecording instrument to be rotated step by step at the same average rateas the continuously rotating type wheel of the sending instrument. Thesynchronizing levers of both instruments are simultaneousiy fed by theirscrews toward the arrestinfr position; and that of the receivinginstrument, having a shorter distance to go, reaches its arrestingposition iirst. The rotating parts of the sending instrument, however,continue until similarly arrested. The type wheels of both instrumentsthen are in correlated zero position; in other words, correspondingcharacters of both are registered with the respective printing hammers.

A message is sent by the operator striking the keys 24 in the samemanner as one would the keys of a typewriter. The rst key displaces thelatch bar 34, releasing the synchronizing key and synchronizing lever,(or, if the synchronizing key had not been just previously depressed,then the key corresponding to the last character of the last previousmessage), and placing itsl associated stop lever 2l in the path of astop corresponding to the letter or character to which the now de-.

pressed key is appropriated. The sending disk rotates through aproportional angle, transmitting a number of Wave groups, equal to thenumber of characters on the type wheel in an angle equal to that betweenthe stop lever 2'! and the nearest stop 38 in the same zone. Theresultant impulses received in the tuned receiving station cause anequal angular movement of the type wheel of that station. When thewheels of both instruments then pause, the switch closing levers ofboth, which have meanwhile been maintained in raised position by thelifting ratchets and retarding escapements, descend and close theswitches 48 and Elfi. A printing impression is This Y made at bothstations and the switches are simultaneously opened.

The retarding escapements here shown are of well known character and arecapable of being adjusted as to their timing function so as to permitdescent of both carrier levers 5i and 98 at the same rate or atdifferent rates as desired. If necessary to insure that each characterwill `be printed at the receiving station before another series ofimpulses are generated at the sending station, the retarding escapementof the sending instrument may be adjusted for greater delay than that ofthe receiving station. But ordinarily this is unnecessary.

In the operation of the let off device of the receiving instrument,withdrawal of lpawl 7S from the ratchet wheel brings pawl 8l into avtooth space at the opposite side and allows the wheel to turn throughthe full spacing of one tooth immediately. When the armature isreleased, pawl 'I9 enters the next tooth space while pawl BI iswithdrawn (by the action of spring 83) but the wheel does not rotate.Pawl 8|, as soon as released from the ratchet wheel, is raised by itsspring 85 ready for re-engagement with the wheel. With each waveimpulse, the ratchet -wheel turns one step and waits for the next imarepetition of the action thus described. As all the stops in any onezone of the sending instrument drum are equally correlated angularlywith the same number or letter on the type wheel, when two or more setsof characters are -provided 0n the wheel, it is immaterial whether thedrum turns througha large or a small angle before being arrested. In anycase the character corresponding to the key depressed is placed inprinting position when the drum is arrested, and

a number of impulses corresponding to the angle of rotation istransmitted to the recording instrument, causing the type Wheel of thelatter to be turned through an equal angle.

At the conclusion of the message both type wheels are left in the lastprinting position and, so long as both remain in correspondingpositions, a further message may be sent and correctly received withoutemployment of the synchronizing means herein described. Suchsynchronizing means, however, overcomes any liability of failure torecord the received message f correctly due to displacement of therecording type wheel'unknown to the sender.

The signal transmission by the instruments just described is eiected byimpulses of equal duration, equally spaced in point of time, the numberof which is equal to the number of spaces on the type wheels betweensuccessiveA letters or symbols of the message. rIhese impulses aretranslated at the receiving station into a printed record the same asthe message transmitted. Where the characters are jumbled, andparticularly when two or more series of characters are provided andthose of one or more sets are arranged out of their conventional order,the nurnber of impulses between pauses affords no logical guide fordecoding the message in case it is intercepted by an interlopingreceiver. But the correlated receiving instrument automatically decodesthe message transmitted with the aid of such jumbled characters.

The transmitted message is receivable only at a station or stationsprovided with selectors tuned to the frequencies of the wave groupsgenerated by the sending phonograph disk. But the same instrument may beused for sending to different receiving stations by the meresubstitution of different disks having recorded tone group frequenciesto which the different stations are tuned. In order to make interceptionmore diilicult, the tone groups of the sending instrument may beaugmented by one or more idle tones which are not intended to affect thereceiving instruments, but will confuse a spy.

The type wheel of the sending instrument is not essential for thetransmission of messages because the drum, or its equivalent, is thecontrolling element which determines thenurnbern of impulses generatedat each stage of transmission. But the type wheel and printingattachment here are desirable as they cause a record to be made at thesame time the message is sent, which may be useful as a check on theaccuracy of the rnes- Sage received.

The speed of message sending is limited by the time required foroperating the relays at the receiving station, which time is in theorder of 1/60 of a second. Hence approximately 60 impulses may betransmitted per second and the control disk is geared to rotate at acorresponding rate, or slower if desired.

The tones produces by the wave groups transmitted with this rapidity andfor correspondingly short periods of time, cause noperceptibleinterference with words or music broadcast at the same time by means ofa radio wave of the same frequency as that used for signal transmission,since their duration is too short to have any disturbing effect on theear of the listener. Hence our system may be used by employment of thesame radio frequencies used for other purposes, and on telephone linesused at the same time for conversations.

The principles of means for selectively and exclusively activatingdifferent receiving stations and recorders are more fully illustrated inFig. 8. This illustrative system is controlled by six different tonesused three at a time. For convenience the tones will be referred to asl, 2, 3, 4, 5 and 6, which may be of any consecutive or nonconsecutivepitches, but all different from one another, The reference charactershere used are the same as in the general diagram of Fig. l, modified byexponents related to the several tones. OJ-b represents the tonegenerator and signal sender, such as that illustrated in Figs. 3 and 4.d is the transmitter of standard character, and c an amplifier which isusually necessary but not an essential factor of the invention. f is thereceiver of standard character and s is a power source such as a batteryor generator capable of furnishing sufficient energy to operate therecording instrument of Figs. 6 and 7 or other recorders. g1 is aselector tuned to the tone l by selective means such as the networkshown in Fig. 2 or equivalent means. Its input side is connected to thereceiver and its output side to a relay 1L11 sufficiently sensitive toclose a switch in the,` power circuit from the power source s whentraversed by the signal transmitting vibrations. g2, g3, g4, g5 and g6are similar selectors tuned to the tones 2, 3, 4, 5 and 6 respectively.Selector g2 is connected with relay b21 and selector g3 with relay 1131.The several recorders are located in the column beneath the reference4letter i, distinguished4 from one another by numbers designating thetene groups which control their operation.

Assuming that the signal generator produces simultaneously the tones l,2 and 3, then through the selectors g1, g2 and 93, the relays 1111, h21and 1131 are simultaneously operated and a circuit is made through therecorder bearing the number 123. In like manner the selector g4 isconnected with relay h11 whereby, if the tone group consists of tones l,2 and 4, the recorder at E24 is actuated. Selector g5 is similarlyconnected with relay 1151 and Q6 with relay 1161, whereby the tone 4 ortone 5 substituted for tone 3 of the tone group causes actuation of therecorder 25 or 26 respectively.

A second relay 1222 is coupled with the selector g2. Other relays,designated by the letter 1L with appropriate exponents are similarlycoupled to the selectors g3, g4, g5 and Q6, and connected in circuit asshown by the diagram So as to cause operation of the different recorderseach by its own appropriate tone group.

To avoid duplication, all of the twenty record ers represented are shownin the diagram as connected by wiring with thirty-four relays and sixselectors, all receiving impulses from a single receiver and power froma single power source. Eut it is to be understood that where thesyscomprises stations separated from one another in space, each stationwill consist of one recorder with its own receiver, power source7 threeselectors and three relays. Any such recorder is operable by vibrationfrequencies to which its selectors are tuned carried by a radio wave towhich its receiver is tunedy provided the impulses so received arepowerful enough to operate its relays.

Where a number of recorders may be located in the same place, as in a reengine station to record alarms sent from scattered boxes, mechanicallycoupled plural switches may be operated by the relays to close one gapin the circuits of all the recorders which are affected by the sametone. Thus, referring to Fig. 9 which illus trates a simple systemcontrolled by six tones, the conductors t1 and t2 represent connectionsfrom the receiver to all of the tuned selectors g1 to 9'1 inclusive.Relay h1, controlled by the selector g1 is connected to close a circuitbetween the conduc-tors u1 and u2 from a power Source s, in which isincluded the magnet of a switch v1. Similarly each of the otherselectors and relays is connected to operate one of the switches o2 too6 inclusive. The switch o1 is adapted to open and close a switchcontact U11 in all of the recorder circuits associated with tone 1. rlheswitch o2 operates circuit closer U21 in circuit with all the recorderscontrolled by both tone l and tone 2; and circuit closer 1:22 in all theother recorder circuits controlled by tone 2. In similar fashion theother switches control circuit closers in the circuits of the severalrecorders, as will be cle-ar from the diagram. Each of the fire alarmboxes or other transmitters corresponding to the recorders hereinindicated by the oblong outlines bearing three-digit numerals, generatesa group of three tones which is imposed on a radio wave. The group oftones for each box is different and distinctive but the radio wavelength and frequency for all is the same. Each box therefore, whenoperated, causes the appropriate one of the recorders at the centralstation to record or indicate its operation.

It may be remarked that for the purposes of j this invention andthe.genericA protection sought,

we make no distinction between a recorder and an indicator, consideringthata recorder is an indicator also and that one is the equivalent ofthe other.

In the foregoing description it has been assumed that the tonesgenerated at the transmitting station are produced simultaneously. Wherethe tones are generated progressively, and may be so generated in anyorder, the number of possible stations in a system using a given numberof tones is factorial G times the number of stations possible with tonegroups generated simultaneously, where G is the number of tones used inthe group. In Fig. l We show how, by the employment of auxiliaryswitches, different stations, each controlled by the same three tones,may be selected exclusively by those tones when produced in differentsequences. As in the preceding gure, t1 and t2 represent the conductorsof the output circuit from the receiver; u1 and u2 represent the linewires from a power source; g1 to g6 inclusive represent selectors tunedto the respective tones; and h1 to h6 inclusive designate therelaysassociated with the several selectors. Let it be assumed that the tonegroup consisting of the tones 1, 2 and 3 generated in that order isreceived at the receiving station. The electrical vibrationscorresponding to tone 1 then operate the relay h1 to close a circuitbetween the lines u1 and u2 in which is included a relay switch ull.This switch then closes a gap in the magnet circuit of switch 'U21 whichis in circuit with the switch of the relay h2. When tone 2 comes to thereceiver this circuit is completed and the switch 'U21 then closes a gapin a circuit which includes the magnet of switch D31 and relay h3;whereby, when tone 3 comes into the receiver all three switches '011,U21 and U31 are closed between the power lines and the recorder orindicator 23. It is necessary that tone 1 persist until tones 2 and 3are received and that tone 2 persist until tone 3 is received. Theremust be an overlapping of the three tones for a time long enough tocause operation of the recorder. The production of these tones insequence causes one impulse to be generated at the recorder, such as theactivation of magnet 'il in Figs. 6 and '7.

If the tone sequence is 2-1-3, for instance, the switch '026 is rstclosed, causing the switch 2212 to be closed when tone 1 is received andswitch 'U36 to be closed when tone3 is received, completing theoperating circuit for the recorder 213. Similarly the same three tonesin the order 3-2-1 cause iirst the switch 12311 then the switch 1128 andfinally the switch 1118 to be closed in succession, operating therecorder 32|.

The relays responsive to other tones are connected with switches inessentially the same manner to operate the indicators at 120 differentstations by diiferent groups and sequences of three tones each. Theconnections for approximately half of these stations are shown in Fig.l0. A suitable extension of the diagram to include the whole series willbe readily apparent to those skilled in the art. In this case, as inFig. 8, the stations havebeen grouped together to save space and avoidduplication of selectors and relays. But in actual practice each stationmay be widely separated and spaced from all others and contain its ownthree selectors, relays and sequence switches.

The same principles are capable of indefinite extension with the use ofa greater number of tones, while stations may be made more selective byusing more than three tones in their controlling tone groups.Equivalents of the several means and instrumentalities hereinbeforedescribed are included within the scope of the protection hereinclaimed, such as other means of vibration generation or tone productionthan the phonograph disk herein illustrated; other means of indicatingor recording than the type wheel illustrated, such as interruptionsproducing dot and dash signals and a marker for printing such signals.And any suitable radio or telephone equipment may be used fortransmitting and receiving the tone frequencies.

The word tone in this description is used as indicating Vibrations,Whether audible or not, which have a definite frequency, whether suchfrequency is that of a musical note of the standard scale or aninharmonious frequency.

What we nclaim and desire to secure by Letters Patent is:

1. The method of communication which consists in generating periodicallya group of vibrations of different frequencies like or analogous to achord of tones, each period consisting of a limited time during whichsuch Vibrations are generated and a time during which no vibrations aregenerated, causing such periodic generation to cease at the conclusionsof diiferent numbers of periods in accordance with a signal code,transmitting such vibrations electrically, transforming the vibrationsinto mechanical motion at a receiving station by power under the controlof a plurality of receivers each tuned to the vibrations of oneparticular frequency, and causing the movements so resulting from thetransformed received vibrations to produce periodic impulses Ycorrelated with the generation of such group of vibrations.

2, The method of communication which consists in modulating a radiocarrier wave by a plurality of vibrations of respectively diierentprescribed frequencies with overlapping of the persistence of suchvibrations of different frequencies in point of time, generating suchmodulating vibrations periodically with persistence during brief periodsof time and intervals between successive generations, sending signals byso producing such modulating vibrations in numbers of periods accordingto a code, receiving the modulating vibrations in different selectors,each tuned to vibrations of a specific frequency, at a receivingstation, combining and transforming the received electrical vibrationsof different frequencies into a mechanical impulse with each period ofreceived vibrations, and causing the successive impulses so producedtoreproduce the message transmitted from'the sending station.

3. The method of communication which consists in producing periodicallyat a sending station a group of vibrations of different frequencies, oneat a time with persistence of the vibrations of each frequency until allthose of the group, have been generated, transmitting such vibrationselectrically to a receiving station, causing the vibrations of eachfrequency to operate a selector tuned to that frequency at the receivingstation, and causing the vibrations of one frequency first received tocontrol the effect produced by subsequently received vibrations of adifferent frequency.

4. A communication system comprising an apparatus for mechanicallygenerating groups of respectively different vibrations with an intervalafter each group, means for controlling the ac.

tion of said generating means to cause generation of different numbersof successive groups in accordance with a prescribed signal code, atransmitter having means for transforming such mechanical vibrationsinto electrical undulations, a receiving station having selectors tunedindividually to the different vibrations of such group, a source ofelectrical energy, relay switches in the circuit of said source, eachunder control of one of said selectors, a motive apparatus in circuitwith said source adapted to produce a mechanical impulse when said relayswitches are closed, a signal instrument, and means operated by saidmotive apparatus for propelling said signal instrument through a numberof successive steps equal to the number of vibration groups generatedwith each action of said generating means.

5. A communication system comprising a mechanical generator ofvibrations having means for producing in regular periodic succession agroup of vibrations of respectively different frequencies with intervalsbetween successive groups, means under the control of an operator foractuating said generator to produce a greater or less number of suchgroups in continuous succession and to intermit such vibrationproduction at the end of a prescribed succession of groups, anelectrical transmitter for transforming and transmitting said groups ofvibrations, a receiver of electrical vibrations, a plurality ofselectors associated with said receiver and each tuned to passvibrations of a given frequency different from the frequency to whichanother of said selectors is tuned, relays each separately operable byone of said selectors, a power source in circuit with said relays, meansconnected for operation by said power source and adapted to produce asingle impulse of mechanical motion when all of said relays areenergized at the same time by vibrations passing through theirrespective selectors, an indicating instrument movable throughsuccessive steps of movement, and means for causing each said impulse tomove the said instrument through one of said steps.

6. A communication system comprising a generator of vibrations havingmeans for producing vibrations of respectively different frequencies insuccessive groups, with the vibrations of one frequency in each grouppreceding and overlapping the generation of the other vibrations of thesame group, and repeating such groups of vibrations with intervalsbetween them, means for propelling said generator and arresting itsaction under control of an operator after production of one or moregroups of vibrations, a transmitter having means for converting suchvibrations into electrica-l vibrations, a receiver of electricalvibrations, a plurality of selectors each tuned to vibrations of aspecic frequency diierent from that to which another selector is tuned,a source of electrical energy, an indicator instrument and a normallyopen switch therefor in circuit with said source of energy, meansoperable by one of said selectors for closing said switch, and meansoperable by another selector for preventing -actuation of the last namedmeans except when such other selector is energized.

7. In a communication system, a receiver of electrical vibrationsresponsive to a range of vibration frequencies, a plurality of selectorsconnected to said receiver each tuned to pass vibrations of a frequencywithin said range and different from the frequency which the otherselector can pass, a source of electrical energy, an electricallyoperated indicator, a'normally open relay switch between said indicatorand the power source, a normally open relay circuit closable by one ofsaid lselectors for actuating the indicator relay, a normally open relayswitch in the circuit between the power source and the saidselectoroperated relay circuit, and means controlled by another selectorfor closing the last named switch, whereby actuation of the indicator ismade possible only when said selectors are energized in a predeterminedorder.

NATHAN H. SUREN. WILLIAM W. CARTER.

